Reactive Ion Etching: Angular Yield & RIE-Lag (2D)

This 2D cross-section companion replaces the 3D version's boolean "is this cell's column open above it" test with two independently computed, geometry-driven quantities. First, a local surface-normal estimate (from the solid/empty density gradient around each cell) feeds an angle-dependent sputter-yield curve, so vertical floors and oblique sidewalls near a beam edge etch at physically different rates instead of a single flat probability. Second, a cosine-weighted view-factor ray cast from every exposed cell to the open plasma above throttles the isotropic chemical etch term as trenches get deeper and narrower — reproducing real RIE-lag (aspect-ratio-dependent etching), a well-documented plasma-etch phenomenon the original cellular automaton's constant chemical rate cannot show. Drag ion collimation from a wide scattered spray to a tight beam and watch both the sidewall angle and the floor's view-factor readout respond in real time.